In 2014 I used this blog to collect ideas for a D&D adventure, which I then wrote with another blogger, and played in my 4E campaign. It is the story of an evil princess who wants to succeed her father on the throne, but the father prefers his younger son. So she uses an incident where a crack into the Underdark opens in the dukedom to make people afraid of the "Underdark menace" to make her brother, who is captain of the guard, look incompetent. The players get involved when the princess has the lover of the prince murdered, and the players become suspects. Trying to get rid of them and creating a panic at the same time, the princess arranges for them to be transformed into deep gnomes. The players need to flee, and have a series of adventures in the wilderness and in the Underdark before gaining their normal form back. Then they return to the city as diplomatic envoys of the king of the deep gnomes to negotiate peace and trade, and try to find out who is behind their transformation and the murder.

The whole story ends in a moral dilemma: The players successfully negotiate peace, and find the henchmen who did the murder and the transformation. They find out that the princess is behind all that, but they can't get proof enough to convince her father. The end of the adventure is open, but the three most obvious options would be to either attack the princess, turn the princess into a deep gnome, or to leave the princess be. None of these options is without negative consequences: Killing the princess risks getting found out and being attacked by the guard. Turning the princess into a deep gnome risks destroying the peace treaty between the dukedom and gnomes (because the princess appears to have been "kidnapped by a deep gnome"). And leaving the princess be results in her eventually murdering her brother and "winning".

I now played the adventure through a second time in 5th edition (where the adventure took 3 sessions instead of 10 in 4E). And the players of the 5E group chose the same option as the 4E group, which is letting the princess win. Personally I found that the worst possible option, but it is the one with the least direct risk for the players. What do they care whether the dukedom in the future will be governed by a good prince or an evil princess? So I think my adventure has a design flaw there. Or do you think other groups would have chosen one of the other two options?

I think this is another example of players being "murder hobos," where they behave as complete sociopaths who always choose the greatest xp/loot reward for the least risk, regardless of other factors. The problem is not something you need to fix in the design of your adventure, but the fundamental behavior of players. I don't know of any solutions for this.

I would definitely look for ways to directly expose her (confession overheard by her father, for example) and then kill/get rid of her in some way. If the option to expose her does not exist, then the Princess will always 'win' because you never provided realistic options to trigger her 'loss'.

In my opinion, a better moral choice would be:1. Get a deal with the Princess to not expose her. The princess wins, but the players get a huge reward.2. Expose her and let her live. The brother wins and the players get a moderate reward.3. Expose her and then kill her or transform her. The brother wins but the players are asked to leave given a minimal reward. The players may opt into this if their feelings towards the antagonist were especially harsh, of if the party is chaotic in alignment.4. Kill or transform her without exposing her. The war continues because she appears like a victim of the deep gnomes. The players make out with some of the princess valuables in the process, this is for Evil parties.

One of the big questions comes down to whether this is an ongoing campaign where the results will matter to the PCs. In a game where the PCs do not feel beholden to this king or kingdom, many of my groups would have "let the princess win".

On the other hand, groups that felt more attached to the kingdom or were more involved in the future of the campaign would have been far more likely to seek a better resolution for the kingdom.

As for your list of answers, Tobold, an option that one of my groups might have picked would have been to build up the prince personally and/or politically so that he could withstand his sister.

For me personally, my first thought was to fabricate evidence against the princess or to seek other genuine crimes she had committed in order to convince her father. The fabrication wouldn't have been evil in some characters' eyes because the princess really was guilty, it was just that her father was a fool.

That's either a flaw in the adventure, or a group that didn't gather enough evidence.If the group found all the evidence available, presented it to the father and he still doesn't believe them, that's on the father. Not the group.

Also before choosing I'd need more info on the dukedom (are they all scum?) and the deep gnomes (are they all scum?) and the transformation process (is it a potion, poisoned air? and do you retain the form on death. Is it easy to perform/reverse)?

Without any of that knowledge my gut reaction is to transform her into a deep gnome. And transform the brother into the princess. :P

Medieval princesses are for marrying off to secure treaties. Propose to marry her to the Deep Gnome King's heir. That removes any problems with the Duke not getting his preferred heir, builds a peace treaty and gives the Princess a karmic punishment.

"If the group found all the evidence available, presented it to the father and he still doesn't believe them, that's on the father. Not the group."

That whole fantasy world exists only in my head and the heads of the players. A problem that isn't the players' problem is in fact not a problem at all. In order to create player agency I need to create situations where the problem is the problem of the group. It is up to the players to come up with a solution, and all solutions are valid. I don't mind whether the players solve the problem by fabricating evidence or scheming to marry the princess to the gnome (wonderful idea!), anything remotely realistic they would have tried would have worked.

@Tobold: you DID create a player agency, you just don't like their answer. The other commenters try to weasel themselves out of the situation by offering solutions that did not exists in the dilemma. While their suggestions can be good for game development (letting you make better adventure next time), they are skipping answering the question.

My answer is that they did the right choice based on the moral statement "do no harm unless you are absolutely sure that you do more good in the same time". Yes, the princess might win. Might not, because someone else can solve the problem they cannot. Fighting the "innocent" princess and the really innocent guards or triggering a war with the nation of the Deep Gnomes surely cause death and destruction with uncertain outcome.

I'm absolutely shocked to be saying this but...I agree with Gevlon. And on a MORAL question too! My god, what is the world coming to...

Honestly, if exposing the princess is flat out not an option (No amount of proof will successfully expose her, or at least if I believe this to be the case regardless of if it is or isn't), I think the most moral option is to let her "win". I wouldn't be happy with it. And if I liked the dukedom, I would probably want to come back and help more if she ever does send it to shit with her own machinations.

But the other two options don't strike me as better, especially given a lack of ability to see into the future. There are too many "maybe"s involved in the negatives of letting her win and the positives of stopping her in the other two listed ways to outweigh choosing anything else. And I didn't even consider the party's own safety and profit in this decision, the third option just appears to be "objectively" better (Not objectively as in I think I have some access to pure morale knowledge that means I personally am picking the right decision, just that I'm not weighing personal benefit or risk into which choice I would go with).

Yeah, I kinda have to agree with Gevlon as well. "The road to evil is paved with good intentions", and all. If they realistically can never convince her father, then the PCs going full G.W. Bush on the princess would only worsen the situation. The only moral solution would be to 'let her be, and maybe in the future she will be dealt with or the truth will be exposed'.